In the field of applied-ignition, liquid-cooled internal combustion engines comprising at least one cylinder head with at least two cylinders, it is known that intake lines which lead to the inlet openings, and exhaust lines which adjoin the outlet openings, may be at least partially integrated in the cylinder head. The exhaust lines of the cylinders are generally merged to form one or more overall exhaust lines. The merging of exhaust lines to form an overall exhaust line is referred to generally as an exhaust manifold. It is well known for the exhaust lines of at least two cylinders to at least partially merge within the at least one cylinder head to form an overall exhaust line, thus forming an at least partially integrated exhaust manifold (IEM). It is also well known for a typical liquid-cooled cylinder head to comprise a plurality of coolant ducts or at least one coolant jacket formed in the cylinder head, in order to conduct the coolant through the cylinder head. The resulting cylinder head structure is complex, as well as a thermally and mechanically highly loaded component.
On account of the ever more dense packaging in the engine bay and the increasing integration of parts and components into the cylinder head as mentioned, the thermal loading of the internal combustion engine and of the cylinder head in particular, is increased. As a result, increased demands are placed on the cooling system and it is imperative that measures be taken to reliably prevent thermal overloading of the internal combustion engine.
To reliably prevent overheating of the internal combustion engine, the cooling capacity of the engine cooling arrangement is designed for operating states with a very high cooling demand or the maximum cooling demand, which are characterized by high loads at low vehicle speeds. For example, operating conditions such as those that occur during acceleration and during uphill driving phases. Under such conditions, the engine cooling system is charged with dissipating a very large amount of heat, without the available air flow needed for sufficient heat dissipation.
Attempts to address thermal overloading of individual components of an internal combustion engine with integrated exhaust manifolds include initiating an enrichment (X, <1) whenever high exhaust-gas temperatures are to be expected. Therein, more fuel is injected than can be fully combusted with the provided air quantity, wherein the excess fuel is likewise heated and evaporated, such that the temperature of the combustion gases falls. However, the inventors herein have recognized potential issues with such systems. In one example, this method is generally unable to provide sufficient cooling to the cylinder head. In another example, fuel consumption and pollutant emissions of the internal combustion engine are increased.
Another possible method for improving cooling capacity for a liquid-type cooling arrangement for an internal combustion engine may include constructing the cylinder heads using materials that may be highly loaded thermally, in particular nickel-containing materials. The inventors herein have recognized that highly thermally loadable materials such as these are costly and that by alternately decreasing the thermal loading of the cylinder head, a less costly and lightweight material (e.g., aluminum) may be utilized for cylinder head construction.
Another method for improving cooling capacity for a liquid-type cooling arrangement may lead to excessively large coolers, or multiple coolers, which necessitate mounting in the front-end region of a vehicle where available space is minimal. It is shown that coolers may already be arranged one behind the other and spaced apart from one another so as to partially overlap.
The inventors herein have recognized the shortcomings of attempting to continually increase either cooler size or quantity to address the ever-increasing thermal loading of the cylinder heads and offer an alternate solution. As one example, the inventors herein do not seek to extract the greatest possible amount of heat from the exhaust gas via the cylinder head. Rather, by introducing thermal insulation at least regionally, the heat transferred into the cylinder head is impeded, whereby the cooling power requirements of the engine cooling arrangement is intentionally reduced. The thermal permeability of the heat-transmitting surface, that is to say of the cylinder head wall, is reduced at the exhaust-gas side. Thereby, heat introduced from the exhaust gas to the cylinder head and subsequently to the coolant system occurs to a lesser extent than on an uninsulated system.
One possible method for improving the cooling capacity for an applied-ignition, liquid-cooled internal combustion engine includes utilizing a thermal barrier on the internal walls of the cylinder head to reduce heat transfer to the cylinder head and the coolant system. One example, shown by Kloft et al. in German Patent No. DE 10 2011 114 771 A1 discloses a general process of adhering metal or ceramic insulative coating on the internal walls of the exhaust ports, but it offers little detail on the most suitable arrangement of the insulation within the ports. In another example, shown by Ford Global Technologies LLC in German Patent No. DE 20 2014 100 387 U1, a process is disclosed for insulating the walls of the coolant jackets in a cylinder head. While the Ford patent makes only brief mention of the possibility of insulating the exhaust ports rather than the coolant jackets, they offer no details as to a suitable configuration of exhaust port insulation. In yet another example, shown by Glanz et al. in German Patent No. DE3915988A1, a sheet metal port insert is disclosed to provide a heat insulative layer in the exhaust port. The use of a separate cast insert involves a separate production effort and complex tooling to ensure proper placement during cylinder head casting.
The inventors herein have recognized problems with the above approaches. In one example, integrating complicated insulating inserts into the casting process may be cumbersome and expensive, while in another example, adding regional or full insulation without justification may result in excessive or unneeded insulation and expense. In other examples, utilizing costly materials to withstand the high thermal and mechanical loads on the cylinder head may not be needed if, alternatively, the heat transfer to the head can be reduced. In yet another example, introducing enrichment for the purpose of cooling decreases fuel efficiency and is ineffective. Due to space constraints in the engine bay, increasing cooler size or adding coolers is often not an option to accommodate an increased heat load on the internal combustion engine. Thus, the inventors herein provide an approach to at least partially address the above issues. In one example, an applied-ignition, liquid-cooled internal combustion engine comprising at least one cylinder head with at least two cylinders, in which each cylinder has at least one outlet opening for the discharge of the exhaust gases via an exhaust-gas discharge system, each outlet opening being adjoined by an individual exhaust line and the individual exhaust lines of at least two cylinders merging within the cylinder head at a collection point to form an overall exhaust line thus forming an integrated exhaust manifold, which overall exhaust line emerges from an outlet flange of the cylinder head, and at least one coolant jacket which is integrated in the cylinder head is provided for forming a liquid-type cooling arrangement, and the exhaust manifold integrated in the cylinder head is, at an exhaust-gas side, provided at least regionally with thermal insulation.
In this way, the thermal insulation is formed in such a way as to reduce heat transfer from the exhaust gas to the cylinder head and the consequent burden on the coolant system. As one example, the thermal insulation may comprise a protective heat shield which may comprise a thermal insulation insert having at least one tongue-like element extending into the overall exhaust manifold as well as at least one thermally insulated runner that extends along the interior walls that define the integrated exhaust manifold at the locations of greatest heat load. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.